Email is good.

Nice little single-serving website.

The solution is not to ask to ask, but just to ask. Someone who is idling on the channel and only every now and then glances what’s going on is unlikely to answer to your “asking to ask” question, but your actual problem description may pique their interest and get them to answer.

So, to summarize, don’t ask “Any Java experts around?”, but rather ask “How do I do [problem] with Java and [other relevant info]?”

I think chat and chat-like software has this problem, where email does not.